摘要/Abstract

银离子可以高效地催化硅烷氧基炔与α,β-不饱和羰基化合物之间的[2+2]环加成反应, 在银离子催化下硅烷氧基炔可以与甲醛的羰基发生[2+2]环加成后开环生成不饱和酯. 利用密度泛函理论(DFT)计算发现, 在这两个反应中银离子与硅烷氧基炔之间相互作用, 将硅烷氧基炔激活成为硅正离子和银烯酮, 硅正离子进一步催化羰基化合物(α,β-不饱和羰基化合物或者醛)和银烯酮之间的[2+2]环加成反应.
关键词: 硅正离子, [2+2]环加成, 银烯酮, 醛的烯化, 硅烷氧基炔
Mechanism of silver-catalyzed [2+2] cycloaddition between siloxy-alkynes and α,β-unsaturated carbonyl compound remains controversial. Based on density functional theory (DFT) calculation, it is revealed that Ag⁺ activate siloxy-alkyne into silver-ketene and silylium ion (TIPS⁺) in this reaction. TIPS⁺ then promote [2+2] cycloaddition between α,β-unsaturated carbonyl compound and silver-ketene to form cyclobutane-intermediate, which undergos TIPS⁺ migration and transforms into final product. The mechanism of Ag⁺ catalyzed olefination of aldehydes using siloxy-alkynes was also investigated, the results showed that TIPS⁺ migration also took place in this reaction. In the two reactions studied, Ag⁺ interacts with π-bond of siloxy-alkynes and triggers TIPS⁺ migration, which offers alternative solution to silylium-catalyzed reaction. As similarity of ynolates, silver-ketenes are more stable, which can undergo 1,4-nucleophilic addition with α,β- unsaturated compound. For [2+2] cycloaddition, catalytic variant is rather limited, this work provides a different perspective to obtain four-membered ring products or its ring-open derivates.
Key words: silylium ion, [2+2] cycloaddition, silver-ketene, olefination of aldehyde, siloxy-alkyne


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